Add JournalD Writer (#57)

JournalD writer decodes each log event and map fields to journald fields. The JSON payload is kept in the `JSON` field.

journald/journald.go

@@ -0,0 +1,112 @@
+// +build !windows
+
+package journald
+
+// This file provides a zerolog writer so that logs printed
+// using zerolog library can be sent to a journalD.
+
+// Zerolog's Top level key/Value Pairs are translated to
+// journald's args - all Values are sent to journald as strings.
+// And all key strings are converted to uppercase before sending
+// to journald (as required by journald).
+
+// In addition, entire log message (all Key Value Pairs), is also
+// sent to journald under the key "JSON".
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"github.com/coreos/go-systemd/journal"
+	"github.com/rs/zerolog"
+	"github.com/rs/zerolog/internal/cbor"
+	"io"
+	"strings"
+)
+
+const defaultJournalDPrio = journal.PriNotice
+
+// NewJournalDWriter returns a zerolog log destination
+// to be used as parameter to New() calls. Writing logs
+// to this writer will send the log messages to journalD
+// running in this system.
+func NewJournalDWriter() io.Writer {
+	return journalWriter{}
+}
+
+type journalWriter struct {
+}
+
+// levelToJPrio converts zerolog Level string into
+// journalD's priority values. JournalD has more
+// priorities than zerolog.
+func levelToJPrio(zLevel string) journal.Priority {
+	lvl, _ := zerolog.ParseLevel(zLevel)
+
+	switch lvl {
+	case zerolog.DebugLevel:
+		return journal.PriDebug
+	case zerolog.InfoLevel:
+		return journal.PriInfo
+	case zerolog.WarnLevel:
+		return journal.PriWarning
+	case zerolog.ErrorLevel:
+		return journal.PriErr
+	case zerolog.FatalLevel:
+		return journal.PriCrit
+	case zerolog.PanicLevel:
+		return journal.PriEmerg
+	case zerolog.NoLevel:
+		return journal.PriNotice
+	}
+	return defaultJournalDPrio
+}
+
+func (w journalWriter) Write(p []byte) (n int, err error) {
+	if !journal.Enabled() {
+		err = fmt.Errorf("Cannot connect to journalD!!")
+		return
+	}
+	var event map[string]interface{}
+	p = cbor.DecodeIfBinaryToBytes(p)
+	d := json.NewDecoder(bytes.NewReader(p))
+	d.UseNumber()
+	err = d.Decode(&event)
+	jPrio := defaultJournalDPrio
+	args := make(map[string]string, 0)
+	if err != nil {
+		return
+	}
+	if l, ok := event[zerolog.LevelFieldName].(string); ok {
+		jPrio = levelToJPrio(l)
+	}
+
+	msg := ""
+	for key, value := range event {
+		jKey := strings.ToUpper(key)
+		switch key {
+		case zerolog.LevelFieldName, zerolog.TimestampFieldName:
+			continue
+		case zerolog.MessageFieldName:
+			msg, _ = value.(string)
+			continue
+		}
+
+		switch value.(type) {
+		case string:
+			args[jKey], _ = value.(string)
+		case json.Number:
+			args[jKey] = fmt.Sprint(value)
+		default:
+			b, err := json.Marshal(value)
+			if err != nil {
+				args[jKey] = fmt.Sprintf("[error: %v]", err)
+			} else {
+				args[jKey] = string(b)
+			}
+		}
+	}
+	args["JSON"] = string(p)
+	err = journal.Send(msg, jPrio, args)
+	return
+}

journald/journald_test.go

@@ -0,0 +1,44 @@
+// +build !windows
+
+package journald_test
+
+import "github.com/rs/zerolog"
+import "github.com/rs/zerolog/journald"
+
+func ExampleNewJournalDWriter() {
+	log := zerolog.New(journald.NewJournalDWriter())
+	log.Info().Str("foo", "bar").Uint64("small", 123).Float64("float", 3.14).Uint64("big", 1152921504606846976).Msg("Journal Test")
+	// Output:
+}
+
+/*
+
+There is no automated way to verify the output - since the output is sent
+to journald process and method to retrieve is journalctl. Will find a way
+to automate the process and fix this test.
+
+$ journalctl -o verbose -f
+
+Thu 2018-04-26 22:30:20.768136 PDT [s=3284d695bde946e4b5017c77a399237f;i=329f0;b=98c0dca0debc4b98a5b9534e910e7dd6;m=7a702e35dd4;t=56acdccd2ed0a;x=4690034cf0348614]
+    PRIORITY=6
+    _AUDIT_LOGINUID=1000
+    _BOOT_ID=98c0dca0debc4b98a5b9534e910e7dd6
+    _MACHINE_ID=926ed67eb4744580948de70fb474975e
+    _HOSTNAME=sprint
+    _UID=1000
+    _GID=1000
+    _CAP_EFFECTIVE=0
+    _SYSTEMD_SLICE=-.slice
+    _TRANSPORT=journal
+    _SYSTEMD_CGROUP=/
+    _AUDIT_SESSION=2945
+    MESSAGE=Journal Test
+    FOO=bar
+    BIG=1152921504606846976
+    _COMM=journald.test
+    SMALL=123
+    FLOAT=3.14
+    JSON={"level":"info","foo":"bar","small":123,"float":3.14,"big":1152921504606846976,"message":"Journal Test"}
+    _PID=27103
+    _SOURCE_REALTIME_TIMESTAMP=1524807020768136
+*/

log.go

@@ -148,6 +148,28 @@ func (l Level) String() string {
 	return ""
 }
 
+// ParseLevel converts a level string into a zerolog Level value.
+// returns an error if the input string does not match known values.
+func ParseLevel(levelStr string) (Level, error) {
+	switch levelStr {
+	case DebugLevel.String():
+		return DebugLevel, nil
+	case InfoLevel.String():
+		return InfoLevel, nil
+	case WarnLevel.String():
+		return WarnLevel, nil
+	case ErrorLevel.String():
+		return ErrorLevel, nil
+	case FatalLevel.String():
+		return FatalLevel, nil
+	case PanicLevel.String():
+		return PanicLevel, nil
+	case NoLevel.String():
+		return NoLevel, nil
+	}
+	return NoLevel, fmt.Errorf("Unknown Level String: '%s', defaulting to NoLevel", levelStr)
+}
+
 // A Logger represents an active logging object that generates lines
 // of JSON output to an io.Writer. Each logging operation makes a single
 // call to the Writer's Write method. There is no guaranty on access